It takes 42 minutes for 10 people to paint 10 walls. How many minutes does it take 17 people to paint 17 walls?
Explanation: Imagine that each person is assigned one wall, and all 10 people begin painting at the same time. Since everyone will finish painting their assigned wall after 42 minutes, it takes one person 42 minutes to paint one wall. If we have 17 people and 17 walls, we can again assign one wall to each person. Everyone will take 42 minutes to paint their assigned wall. In other words, it takes 42 minutes for 17 people to paint 17 walls.